Problem: The arithmetic sequence $(a_i)$ is defined by the formula: $a_i = 3 + 3(i - 1)$ What is $a_{9}$, the ninth term in the sequence?
Solution: From the given formula, we can see that the first term of the sequence is $3$ and the common difference is $3$ To find $a_{9}$ , we can simply substitute $i = 9$ into the given formula. Therefore, the ninth term is equal to $a_{9} = 3 + 3 (9 - 1) = 27$.